Purification (Kitab Al-Taharah)
Dawud :: Book 1 : Hadith 280
Narrated Fatimah daughter of AbuHubaysh:
Urwah ibn az-Zubayr said that Fatimah daughter of AbuHubaysh narrated to him that she asked the Apostle of Allah (peace_be_upon_him) and complained to him about the flowing of (her) blood. The Apostle of Allah (peace_be_upon_him) said to her: That is only (due to) a vein: look, when your menstruation comes, do not pray; and when your menstruation ends, wash yourself and then offer prayer during the period from one menstruation to another.